The present invention relates to a flexible pressure resistant cover, which may be installed on the articulable portion of any flexible endoscope or other medical instrument, which requires a covering of the articulation system.
Medical endoscopes provide a means to view interior areas of the body. To change the direction of view, endoscopes include a mechanical articulation system at their distal viewing end. The proximal end of the endoscope includes means for controlling the articulation system. Endoscopes must be sterilized or disinfected between uses so as not to pass contaminates to patients. Ethylene oxide gas (EtO), Steris, or other systems may be used to sterilize endoscopes. These systems subject an endoscope to significant pressure changes and/or expose the endoscope to fluids that could damage the endoscope""s components. In the case of an EtO sterilization system, conventional deflection covers fail starting at about 7 psi pressure differential. These changes and conditions are significant enough that endoscopes typically include a relief valve to prevent failure of the deflection cover and other components.
A person must manually open or close the relief valve, depending on the sterilization procedure. In the open position, the relief valve balances the internal pressure in the endoscope with the external pressure of an EtO sterilization system to preserve the structural integrity of the instrument. In the closed position, the valve keeps harmful fluids from entering the endoscope and damaging endoscope components in a Steris sterilization system.
More particularly, if the valve is not open during EtO sterilization, the cover over the articulation system is prone to rupture, subjecting the internal components of the endoscope to damage. If the valve is not closed during Steris or other cold sterilization procedures, then fluid can enter the instrument to damage the endoscope""s internal components. Modem endoscopic instruments can cost thousands of dollars making any damage to them a matter of serious consequence.
It is also desirable to eliminate the relief valves because such valve systems add significantly to the cost of producing an endoscope. The opening and closing of a relief valve also complicates the use of the endoscope.
One attempt to overcome the disadvantages of relief valve-based endoscope system is seen in Kobayashi, et al, and U.S. Pat. No. 5,394,864. The ""864 patent describes a cover for the articulable system of an endoscope comprising a pair of inner and outer tubes forming a double-walled tube. A braided tubular material is sandwiched between the inner and outer tube. A second braided tubular material may be disposed between the inner surface of the inner tube and the outer surface of the articulation system.
There are several disadvantages to a deflection cover according to a multiple layer construction. A multiple layer construction adds thickness to the endoscope; thickness is undesirable in minimally invasive surgical procedures. The added thickness may compromise the flex characteristics of the overall structure. An inflexible structure will impede the articulation of the endoscope""s tip, rendering it more difficult for a surgeon to view the surgical site.
A multiple layer construction is also more prone to problems such as breakage and delamination during repeated bending cycles of the endoscope tip. Additionally, if the outer layer is damaged, contaminates may become encapsulated between it and an inner layer. Contamination of this nature is difficult to remove. The risk that one of these drawbacks will materialize is heightened by the relatively harsh and demanding nature of the surgical and sterilization environments for the endoscope.
It should be added that the use of a braided material in a deflection cover tube is undesirable because such material not only reinforces by restricting radial flex, but it also restricts longitudinal flex. Longitudinal flex is, in fact, desirable in a deflection cover because it facilitates bending. It is also worth noting that construction of a deflection cover will be simpler and less expensive the fewer layers it has.
For the foregoing reasons, there is a need for a novel and improved endoscopic deflection cover that provides a pressure resistant seal during standard disinfection and sterilization procedures so that relief valves can be eliminated from endoscopes. In addition to providing a pressure resistant seal around the articulation system, the deflection cover must have appropriate flex and wear characteristics, so that the cover does not interfere with the articulation of the endoscope""s viewing tip or breakdown under repeated cycles of use. The deflection cover must also be made from medical grade, biocompatible materials that can be inserted into a patient""s body without causing trauma, allergic reaction, toxicity, and without carrying harmful biological agents. The deflection cover also should not add unnecessarily to the thickness of the endoscope.
The present invention overcomes the disadvantages of the prior art by providing a pressure resistant deflection cover with adequate and selectable flex characteristics. The pressure relief valve need not be included on endoscopes incorporating a deflection cover made according to this. It may be based on a single layer of polymer tubing. The single-layer construction enables the thinnest possible profiles for the deflection cover, which is desirable in minimally invasive surgical procedures.
In one embodiment, the deflection cover comprises a tubular covering that includes a reinforcement structure, such as, wire, fiber, thread, or threadlike structures of an appropriate tensile strength. The reinforcement structure is preferably impregnated in the tube and oriented to provide predetermined directional flex characteristics to the deflection cover. In one preferred orientation, the reinforcement structure allows some longitudinal flex in the tube while restricting radial flex. This may be accomplished, for example, by impregnating nylon thread helically around the longitudinal axis of the cover.
In another novel embodiment of the invention, a deflection cover comprising a tubular covering formed from single layer or wall of material does not require any impregnated thread or other reinforcement structure. Instead, the deflection cover may be based on a single layer of tubing having appropriate material properties. A suitable tubing is SIL-KORE tubing by W. L. Gore.
A deflection cover made according to this invention can withstand pressure differentials typically encountered in conventional EtO sterilization systems. The deflection cover""s pressure resistance exceeds 7 psi and is at least as high as 14.7 psi.
To provide a deflection cover with adequate flexibility and minimum wall thickness, it is contemplated for most materials that the ratio of the outer diameter of the cover to the wall thickness be at least about 5. Preferably, the ratio is in the range of about 15 to about 30. To fit commercially available endoscopes the length of the deflection cover should be about 30 mm to about 200 mm. The cover may be adapted to fit endoscopes that may be developed above and below this range as well.
To minimize friction against tissue or other surfaces, and to reduce the risk of hosting microbes or contaminants, the outer surface of the deflection cover should be smooth and non-porous.
The deflection covers of this invention may be attached to an endoscope using conventional bonding techniques.